There has heretofore been known a drive apparatus of a vehicle including a differential device through which an output of a drive power source, such as an engine or the like, is distributed to a first electric motor and an output member, and a second electric motor disposed between the output member and drive wheels. Such drive apparatus for a hybrid vehicle is disclosed for example in the Patent Literature 1 (JP 2000-2327A). It includes a differential mechanism being comprised of a planetary gear unit and performing a differential action for mechanically transmitting a major part of power outputted from the engine to drive wheels. A remaining part of power from the engine is electrically transmitted from the first electric motor to the second electric motor using an electrical path. Thus, the drive apparatus operates a transmission of which shifting ratio is electrically changed, for example as an electrically controlled continuously variable automatic transmission. The drive apparatus is controlled by the control device so that the vehicle runs with the optimum operation state of the engine, thus improving fuel consumption, i.e., mileage.
However, for a hybrid vehicle drive apparatus such as that disclosed in Patent Literature 1 to be controlled as a transmission which electrically changes the shifting ratio, the first electric motor bears a reaction torque against an input torque, such as an output torque of the engine (referred to hereinafter as “engine torque”), that is inputted into the drive apparatus. The first electric motor is required to have a reaction torque capacity that corresponds to the engine torque. In order to increase the reaction torque born by the first electric motor in accordance with an increase of the engine torque, etc. demanded for example to obtain a desired running performance, the first electric motor had to be made larger in size as the engine was made higher in the output.
In other words, if a large-sizing of the first electric motor is difficult from the standpoint of installation in the vehicle, the first electric motor may not bear the reaction torque against the engine torque and the durability thereof may be lowered or degraded. The large-sizing prevention and durability maintenance of the first electric motor are incompatible with each other, and cannot readily be realized at the same time.